Aspiration catheters are used commonly in connection with interventional vascular procedures such as angioplasty, atherectomy, stent placement, and the like to aspirate debris that may result from an interventional procedure. They also are useful in removing thrombus (clot masses) that may be present in a blood vessel before the interventional catheterization procedure is initiated and also are used to remove clots whether or not other intravascular procedures are intended or have been performed. Such procedures are referred to as aspiration thrombectomy or aspiration embolectomy. The existence of such thrombotic material in the vessel may present significant medical risk if the clot migrates downstream with the blood flow. Thrombus may also form on the luminal wall of the vessel and cause a clinically significant, even a total occlusion. The different types of material that are aspirated by catheters will be variously referred to hereinafter as clot or intravascular material or intravascular matter.
The aspiration catheter must be of a length sufficient to reach the targeted region of the intravascular site from the location of percutaneous entry into the vascular system. For coronary procedures using percutaneous entry in the region of the groin to access the femoral artery, the length of the catheter is typically of the order of 160 centimeters. If it is determined that aspiration should be performed before an interventional procedure the distal end of the catheter is navigated to the region of intended aspiration, for example, to the location where an intravascular blood clot has been determined to exist. With the distal end of the catheter in position, suction is applied at the proximal end of the catheter to engage the clot by suction to draw the clot into the distal end of the aspiration catheter. The terms suction, vacuum, partial vacuum, reduced pressure and negative pressure are all used interchangeably in the field of medical devices. Typically, the reduced pressure in the aspiration lumen of the catheter is caused by connecting a syringe to the aspiration lumen at the proximal end of the catheter and then retracting the plunger in the barrel of the syringe to build up negative pressure in the aspiration lumen over the length of the catheter.
Among the difficulties that may be encountered in the use of an aspiration catheter is that the amount of suction developed at the distal tip is diminished from that applied at the proximal end of the aspiration lumen as a result of fluid resistance associated with fluid flow through the length of the catheter. The loss of suction may be especially problematic when trying to dislodge and aspirate intravascular material such as a blood clot, particularly a mature clot that has adhered to the inner vascular wall and may resist aspiration.
It would be desirable to provide an aspiration catheter that overcomes the inherent loss of suction over the length of the catheter such that a greater aspirating force can be applied by a catheter distal inlet port directly to the intravascular matter to be aspirated. It is among the objects of the invention to provide such catheters.